I don't know what your prefered instrumentation books say about the Natural Horn and applying natural horn technique on the valved horn. It is not easy to fully understand for a composer, and needs some deeper studies. The internet is also very sparse with Instrumentierung & Instrumentenkunde
Here some links for you:
Hornharmonics
http://www.wordiq.com/definition/Image:Hornharmonics.jpgDefinition of French horn
http://www.wordiq.com/definition/French_horn
Applying Natural Horn Technique to Modern Valved Horn Performance Tractice
Heidi F. Wick. Dissertation
http://www.ohiolink.edu/etd/view.cgi?osu991314575
The Dissertation
http://www.ohiolink.edu/etd/multiview.cgi/osu991314575/Dissertation.pdf
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A professional book written for composers is:
Lehrbuch der Instrumentation und Instrumentenkundeby Herman Erpf
B. Schott's Söhne, Mainz 1959
ED 2609
ISBN 3-7957-221-X
This book will explain all what you have to know as a composer about instruments. It is the full curriculum text of a professional education at a music academy, also the first text i learned. Normally the text of a professor is not available in book form, but you write your own hand written copy during lecture. I don't think something similar exists in another language then german.
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